1. Field of the Disclosure
The present disclosure relates to an optical pumping type vertical external cavity surface emitting laser (VECSEL), and more particularly, to a VECSEL aligned with a pump laser on a single heat sink in one piece.
2. Description of the Related Art
Among semiconductor lasers, an edge emitting laser emits a laser beam in a horizontal direction to a substrate, and a surface emitting laser or vertical cavity surface emitting laser (VCSEL) emits a laser beam in a vertical direction to a substrate. Since the VCSEL oscillates in single longitudinal mode of a very narrow spectrum and emits a beam having a small radiation angle, it has advantages wherein coupling efficiency is high and integration with other devices can be readily achieved. However, a conventional VCSEL makes single transverse mode oscillation difficult in comparison with an edge emitting laser. Further, since single transverse mode operation of the conventional VCSEL requires a small oscillation region, the output is low.
To retain the advantages of the VCSEL while adding high emission power, a vertical external cavity surface emitting laser (VECSEL) has been developed. The VECSEL has an increased gain region by replacing an upper distributed Brag reflector (DBR) with an external mirror so that the VECSEL has a high emission power in the range of several to several tens of watts or more.
FIG. 1 is a schematic sectional view of an optical pumped VECSEL according to the related art. Referring to FIG. 1, a conventional optical pumping type VECSEL includes a laser chip 10 for laser oscillation, a heat sink 20 on which the laser chip 10 is attached through a bonding layer 21, and an external mirror 22 spaced a predetermined distance apart from the laser chip 10. The VECSEL further includes two pump lasers 25 and 26 arranged at both sides at angles to provide pump laser beams to the laser chip 10. The laser chip 10 includes a distributed Bragg reflector (DBR) layer 16, an active layer 18, and an anti-reflection layer 12 that are sequentially stacked on a substrate 14. As known to those of ordinary skill in the art, the active layer 18, for example, has a multi quantum well structure with a resonant periodic gain (RPG) structure and emits light at a predetermined wavelength when activated by a pump laser beam. The heat sink 20 cools the laser chip 10 by dissipating heat generated from the laser chip 10. The pump lasers 25 and 26 emit light at a wavelength shorter than that of the light emitted from the laser chip 10 to the laser chip 10 through lenses 27 and 28 in order to activate the active layer 18 of the laser chip 10.
In this structure, when light emitted from the pump lasers 25 and 26 at a relatively short wavelength is incident on the laser chip 10 through the lenses 27 and 28, the active layer 18 of the laser chip 10 is activated to generate light at a specific wavelength. The light generated from the active layer 18 is repeatedly reflected between the DBR layer 16 of the laser chip 10 and the external mirror 22 through the active layer 18. Therefore, a resonance cavity of the VECSEL is defined between the DBR layer 16 of the laser chip 10 and a concave surface of the external mirror 22. Through this repetition of the reflection, the light is amplified in the laser chip 10, and then a portion of the light is outputted to the outside as a laser beam through the external mirror 22 and the other portion of the light is reflected again to the laser chip 10 as pump light.
However, the conventional VECSEL with the aforementioned structure requires additional heat sinks to cool the pump lasers 25 and 26 besides the heat sink 20 cooling the laser chip 10. Therefore, the laser chip 10 and the pump lasers 25 and 26 cannot be combined into a single module, and this leads to a limitation in reducing the overall size of the VECSEL. Further, an additional process is required to align the laser chip 10 and the pump lasers 25 and 26. Furthermore, in practice, it is difficult to precisely align the laser chip 10 and the pump lasers 25 and 26. As a result, the overall manufacturing process of the VECSEL is complicated and is lengthened. Therefore, it is difficult to mass produce the VECSEL, and the manufacturing cost of the VECSEL increases.